Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.


  1. Advanced Patent Search
Publication numberUS5061500 A
Publication typeGrant
Application numberUS 07/350,217
Publication dateOct 29, 1991
Filing dateMay 11, 1989
Priority dateOct 1, 1986
Fee statusLapsed
Publication number07350217, 350217, US 5061500 A, US 5061500A, US-A-5061500, US5061500 A, US5061500A
InventorsAbraham H. Mendenhall
Original AssigneePackaging Concepts, Inc.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Easy opening microwavable package
US 5061500 A
An improved microwavable package of laminar construction, having its inner layer constructed of a film whose inherent seal strength is sufficiently high that the inside of the package need not have extraneous reinforcement to maintain its integrity filling, storage, distribution and cooking. The microwavable package is ventable and easily opened by virture of a strip of heat sealable adhesive coated along its top edge immediately inside the opening of the bag and having a seal strength less than that of the package formed seals, to mask the package's normal seal strength.
Previous page
Next page
Having thus described the invention what is claimed and desired to be secured by Letters Patent is:
1. An easy opening, ventable bag that is sufficiently microwave transparent for use in heating food contained therein in a microwave oven, said bag comprising a multi-layer laminate film folded into a series of walls, including bottom and side walls each joined to form said bag by a manufacturer's joint and bottom wall seals provided in both the side walls and bottom wall thereof, said side walls having a sealable opening at the top of the bag, said multi-layer laminate comprising at least an innermost, heat sealable layer and an outer layer for the bag walls, said layers forming said multi-layer laminate being calendered together at a laminator station before the bag is formed, said outer layer of said laminate comprising either paper or a polymer film, said innermost layer comprising a heat sealable polyester composite film, said bag further comprising a strip of heat-sealable adhesive coating having its own seal strength less than that of said bag innermost layer heat seal strength, said strip being printed onto said innermost layer of said laminate proximate the top edge of the side walls of the bag thereof before said bag is formed, said adhesive being present in an amount sufficient to mask the heat sealability of said innermost layer of heat-sealable film at said top edge thereof, said heat-sealable strip of adhesive comprising a resin base adhesive formed of polyvinyl alcohol, said printed heat-sealable strip of adhesive being sealed to itself across the open top of the bag to seal closed said top opening of said bag with a food to be microwave heated contained therein, said printed heat-sealable strip of adhesive being sealed to itself across the bag to a degree and present in an amount sufficient to seal the opening into a closure, but which is capable of venting steam through said sealed adhesive strip when steam is created during cooking but which masks the heat sealability of said innermost layer of film and is sufficiently weak to allow the package to be easily peeled open at said top seal after cooking, said venting occurring without sacrificing and rupturing of the manufacturer's joint and bottom seal of the bag.

The subject matter of this application is a continuation of the application having Ser. No. 44,642, filed on May 1, 1987, now abandoned, which in turn is related to and comprises a continuation-in-part of the patent application to the same inventor filed on Oct. 1, 1986, Ser. No. 913,964, now abandoned, upon Microwavable Package Incorporating Controlled Venting, and owned by a common assignee.


This invention relates to a package for use in the microwaving of cookable items, such as popcorn, other food products, or other substances, and more specifically pertains to the easy opening feature of such packages wherein the packages at the top opening are characterized by a peelable seal, which seal is strong enough to maintain the closure as against the heat required for cooking and pressure generated thereby, but which nevertheless is permeable to steam, thus allowing the bag to vent itself, and furthermore, is a sufficiently releasable seal to permit consumers to peel open the package conveniently without exerting undue force.

Another key aspect of prior art microwavable packages, aside from the ventable easy opening closure, is that the package maintains its integrity during filling, storage, distribution and cooking. The package must be sufficiently impervious to cooking oil that it will not weep or bleed oil during a reasonable grocery store shelf life at room temperature, nor during the ensuing cooking and serving usage of the package. The package must not rupture or prematurely open during cooking by virtue of heat and/or pressure in the package during its shelf life. Also, the side and bottom walls of the package, unlike the top closure, must provide a proper barrier against moisture or steam permeation.

Previously, in order to accommodate the broad and comprehensive attributes of a microwavable package, particularly for popcorn, it has been necessary to construct such packages or bags of laminar materials having at least an inner lining or layer and an outer layer for each of the side and bottom walls of said package or bag. The inner layer's fabrication has been restricted to a particular film such as a polyester which is one of the only films commercially available which can withstand the heat of the microwave cooking while also having the tendency to break or peel away at the top during cooking to provide venting and easy opening of the package by the consumer subsequent to cooking.

However, such film materials are characterized by having such low seal strength along the side wall and bottom edges and seals of the package that it has been necessary to reinforce such packages with paper-to-film adhesion in order to prevent bleeding, weeping and other deleterious breakdowns in the package integrity, and to give strength to the package in general. Consumers have even been known to use supplemental wrapping of such bags to prevent moisture permeation and manufacturers have also restricted the types of foods which they package in such easy opening or as sometimes referred to as self-opening style (SOS) microwavable bags.

Various U.S. patents disclosing miscellaneous types of microwavable packages for popcorn and the like which have easy opening features include the following: U.S. Pat. No. 4,571,337; U.S. Pat. No. 2,865,768; U.S. Pat. No. 3,973,045; U.S. Pat. No. 3,052,554; U.S. Pat. No. 4,358,466; U.S. Pat. No. 2,189,174; U.S. Pat. No. 3,851,574; U.S. Pat. No. 4,292,332; U.S. Pat. No. 2,633,284; U.S. Pat. No. 3,478,952; and U.S Pat. No. 3,511,746.

It would therefore represent a substantial advancement in the art if a microwavable bag were provided which would be ventable and easily opened at its top closure without the need for additional structural materials to reinforce the bag against absorption of moisture and/or oil during storage, cooking, subsequent heating and/or distribution or filling of the microwavable bag, and which bag could or would be resistant to other deleterious breakdowns to its structural integrity.


It is, therefore, a principal object of the present invention to provide a microwavable bag, which has the attributes of resistance against absorption of the food, its oil, or its moisture into the bag, either during storage, filling, cooking, shipment or distribution of the product, or during subsequent heating, while at the same time, providing a moisture barrier against either the entrance of moisture into the bag, which may under usual circumstances cause deleteriousness to the food stored therein, or allow moisture to escape from the bag, causing its deterioration.

It is a further object of this invention to provide a microwavable bag which retains its seals, throughout its periphery, even during and subsequent to microwaving, while at the same time, affording sufficient venting and an easy opening closure at the top of said bag without the need for extraneous reinforcements either inside or outside of the bag in the way of supplemental wrappings.

It is another object of the invention to provide an easy opening, peelable closure at the top edge of a microwavable bag without the need for employing an inner liner of film whose seal strength would normally be inferior.

It is a further object of the present invention to permit the use of a wide variety of high seal strength films as the inner layer while also providing for a closure at the top edge of such packages which may be easily opened and ventable to internal steam from the package.

Another significant object of this invention is to provide an upper seal of adhesive that masks the normal stronger seal that is attained between the film(s) forming the microwavable package.

These and other objects may become more apparent to those skilled in the art upon reviewing the summary of this invention and upon undertaking a study of the description of the preferred embodiment, in view of the drawings.

This invention generally provides a multi-laminar structured bag, having either a paper or polymer outer coating, and an inner film layer impervious to moisture and non-wicking coating over the inner layer and at the top edge of the microwavable package incorporating an adhesive seal sufficient to seal the opening into a closure which is ventable but which masks the heat sealability of the inner layer of film sufficiently to be easily opened by the consumer.


In referring to the drawings, FIG. 1 provides an isometric view of the calendar rolls of laminant and the station for applying adhesive, the station for laminating, the station for printing the upper adhesive strip, the station for forming the laminated sheet into the tubular form, the station for cut-off and bottom fabrication, and a further view of the final bag; and

FIG. 2 is a broader isometric view of the finished bag.


In general, the package or bag of this invention is of a size suitable to accommodate the food to be packaged and in a shape of standard self-opening style bag configuration. This normally is a package which has a series of walls, namely, side walls S1 and S2 a bottom wall B. There may be a back and front wall E and F together with gusseted formed side walls. All of the walls are sealed together into a permanent structure, leaving however an opening at the top of said package. This opening is sealed into closure, as through heat and pressure sealing, or the like, after the food or other substance is deposited therein, for eventual cooking. The bag is primarily made of multiple plys or laminants comprising at least an outer liner for the bag, and an inner liner of which will be subsequently described. Other layers may include an inner lining and to enhance the heat sealing characteristics of the bag, a fourth layer or coating may be added onto the interior of the inner ply. It is an essential feature of the present invention that a strip of heat sealable adhesive be coated at the top edge of the opening on its inner side, which seal strength shall form the characteristic peelable and easy opening feature of the present invention.

The inner ply or layer is composed of a film suitable to withstand the heat generated in the microwave oven when in contact with selected foods such as popcorn kernels. Then the inner layer should be non-wicking and impervious to moisture. Its seal strength with the applied adhesive strip is less than that obtained from the standard formed mylar lined bag. Such suitable films for the liner may be, for example, Mellinex polyester film, having a crystalline and polyester base and including an amorphous polyester substituent coextruded therewith. The Mellinex film composition is available from I.C.I. Americas, Inc. of Wilmington, Del. As previously stated, the inner layer should be non-wicking and heat-sealable, in those required areas proximate to the sides, or at the manufacturer's joint for the bag, at its bottom segment, and also along the top edge thereof, which in the present instance, will be coated with a strip of heat-sealable adhesive, as aforesaid, to mask the normal seal strength of the inner layer in order to accommodate the easy opening and closure after the package has been filled with its contents. This strip of heat-sealable adhesive will be explained subsequently.

The outer layer of laminar material forming the structured bag is preferably paper, glassine paper, or polymer film, suitable for use in a microwave oven such as a polyester film available from a wide range of film manufacturers. Usually, but not necessarily, where paper is used it may be oil-stain resistant treated such as with the standard type of treatment readily available.

A middle or intermediate ply may also be employed, and may be formed of a film, paper, glassine paper, Kraft paper, or the like suitable to be laminated to the inner ply in such a way as to form a middle barrier. Such film may be a polyester crystalline type, such as Mylar, or a coated paper, such as glassine type, or a polypropylene. The purpose of these films is to provide an additional moisture barrier as against the migration of moisture into the bag, but yet remain compatible with the heat requirements of the specific food being packaged and subsequently heated and cooked by the microwave energy.

As previously described in accordance with this invention, a registered printed strip of heat sealable adhesive appears on the top edge proximate the opening of the bag in order to form a closure. The heat sealable adhesive is compatible to the substrate of the inner layer and formulated to mask the heat sealability of the inner layer of film so as to replace that heat seal capability with the heat seal characteristics of the adhesive itself. Such adhesives may be for example a resin base adhesive. It is preferable to employ an adhesive made of a polyvinyl alcohol or PVA. One source of such adhesive is Ajax PVA, and sold under the trade name Ajax, by Ajax Adhesives of Chicago, Ill. The seal strength of the adhesive should be no greater than or less than the liners to which it is applied. Such a seal strength will furnish the strip of adhesive with such strength that it remains closed during storage, distribution and cooking, while at the same time, being sufficiently pervious to steam to allow its venting when created during cooking. Yet it is a weak enough seal that it allows the consumer to easily open the package after cooking. This easy opening characteristic may be described as peelability, and emulates the type of seal previously obtained from heat sealable films made by DuPont, such as polyethylene, and sold as DuPont 500 L. However, since this current seal of adhesive printed strip only occurs at the upper closure point of the microwable bag, the inner layer itself may be composed of far stronger seal strength film than the DuPont film, and accordingly, eliminates the need for additional reinforcement through the addition of supplemental package reinforcing structural materials.

In accordance with the manufacture of the microwavable bag of the present invention, a series of aligned equipment is provided and is adapted to include a station for adding a registered printed strip of adhesive along the laminated sheet of packaging material at intermediate positions designed to represent the intended top edge of the package. At FIG. 1, the outer layer 1 may be laminated onto the inner film 2, with an adhesive 3 being applied as shown, and the layers being calendered through the laminator station 4 in order to form the composite laminated sheet 5. At station 6 locates an adhesive strip printer for printing an adhesive segment 7, as previously explained, onto the laminated sheets proximate to where the top edges of the bags may be located. The combined sheets then proceed through machinery, as noted, to form the co-laminated sheet into a four-sided tube 8. The tube is progressively cut at station 9 and a bottom formed at 10 in order to result in the finished bag 11. Normally, the bags are gusseted at their sides by suitable equipment.

At FIG. 2, the adhesive strip 7 for forming a seal at the top closure of the bag may be observed.

Obviously, the microwave bag of this invention may be formed of more than a pair of laminated sheets, as previously explained, and may in fact be fabricated from a series of plies forming an inner, intermediate, and outer laminated sheet, in the manner as previously explained in this application. Although it is likely that a single layer(s) of sheet could form the package. In any event, the printing of the adhesive strip by means of a gravure roll, as at 7, for the purpose of orienting the final top seal for the fabricated bag will be yet applied upon the upper surface 12 of the laminated sheet, before the bag is formed, and will, in effect, be the same as printing that adhesive composition onto what will be the intended interior side of the inner laminated film that eventually forms the interior of the configured bag.

Variations or modifications to the structure and assembly of this invention may occur to those skilled in the art upon reviewing the subject matter of this disclosure. Such variations or modifications, if within the spirit of this invention, are intended to be encompassed within the scope of any claims to patent protection issuing upon this invention. The depiction of the invention in the preferred embodiment, and its disclosure in the drawings, is primarily set forth for illustrative purposes only.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2237327 *Mar 7, 1940Apr 8, 1941Benjamin C Betner CompanyMethod of and apparatus for making bags
US2595708 *Sep 1, 1948May 6, 1952Ivers Lee CoVented package
US2633284 *Mar 28, 1949Mar 31, 1953Mcfarland John CSealed cooking container for comestibles
US3052554 *Nov 16, 1960Sep 4, 1962Colman Benjamin WPopcorn package
US3108881 *Mar 5, 1959Oct 29, 1963Continental Can CoMethod of packaging food
US3204760 *Oct 10, 1962Sep 7, 1965Poly Pak Corp Of AmericaPackages
US3261140 *Aug 30, 1963Jul 19, 1966Continental Can CoMicrowave sterilization and vacuumizing of products in flexible packages and apparatus therefor
US3293048 *Feb 24, 1964Dec 20, 1966Kitterman Donald MFood and beverage cooking container and method of using same
US3314591 *Feb 16, 1966Apr 18, 1967Reynolds Metals CoPouch construction
US3637132 *Jan 9, 1970Jan 25, 1972Oscar S GrayPressure release package or container
US3716180 *Jun 1, 1970Feb 13, 1973Robalex IncPackaging
US3716369 *Aug 5, 1970Feb 13, 1973S PerlmanProcess for cooking foods in polyalkylene teraphalate film bag
US3865302 *Nov 10, 1972Feb 11, 1975Du PontContainer for cooking food therein
US3935810 *Nov 30, 1973Feb 3, 1976Arvey CorporationPouches
US3997677 *Feb 7, 1975Dec 14, 1976Standard Packaging CorporationHigh temperature resistant hermetically sealed plastic tray packages
US4013798 *Dec 24, 1975Mar 22, 1977Teckton, Inc.Selectively ventable food package and micro-wave shielding device
US4141487 *Mar 29, 1977Feb 27, 1979Union Carbide CorporationDisposable food package
US4261504 *Sep 21, 1979Apr 14, 1981Maryland Cup CorporationHeat-sealable, ovenable containers
US4358466 *Jul 28, 1980Nov 9, 1982The Dow Chemical CompanyFreezer to microwave oven bag
US4404241 *Dec 19, 1979Sep 13, 1983James River-Dixie/Northern, Inc.Microwave package with vent
US4456164 *May 18, 1982Jun 26, 1984Keyes Fibre CompanyDeliddable ovenable container
US4461031 *Mar 10, 1981Jul 17, 1984Bagcraft Corporation Of AmericaTubular bag and method of making the same
US4571337 *Jul 1, 1985Feb 18, 1986Hunt-Wesson Foods, Inc.Container and popcorn ingredient for microwave use
US4667453 *Oct 9, 1986May 26, 1987Fres-Co System Usa, Inc.Method of forming sealed flexible container with non-destructive peelable opening
US4691374 *Feb 19, 1985Sep 1, 1987Golden Valley Microwave Foods Inc.Cooking bag with diagonal gusset seals
US4705707 *Dec 17, 1985Nov 10, 1987Presto Products, IncorporatedPolyethylene/polyester nonoriented heat sealable moisture barrier film and bag
US4716061 *Dec 17, 1985Dec 29, 1987Presto Products, IncorporatedPolypropylene/polyester nonoriented heat sealable moisture barrier film and bag
GB697723A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5200590 *Dec 5, 1991Apr 6, 1993Raytheon CompanyApparatus and method for making microwave popcorn
US5385426 *Mar 5, 1993Jan 31, 1995Omann; James S.Apparatus, method and use for reduced shingles
US5451003 *Jul 5, 1994Sep 19, 1995James S. OmannMethod for producing a reduced shingle material for use as a patch and paving matter
US5462166 *Feb 14, 1994Oct 31, 1995The Procter & Gamble CompanyPackage seal for individually packaged sanitary napkins
US5464969 *Nov 10, 1994Nov 7, 1995Curwood, Inc.Self-venting microwaveable package and method of manufacture
US5786010 *Jul 22, 1994Jul 28, 1998American Packaging CorporationBag and method of making the same
US5814382 *Sep 7, 1994Sep 29, 1998American Packaging CorporationBag and method of making the same
US5873221 *May 5, 1997Feb 23, 1999Sealed Air Corporation (U.S.)Foam in bag packaging system
US5913603 *May 5, 1997Jun 22, 1999Sealed Air Corporation (U.S.)Mixing device for foam-in-bag packaging system
US5996782 *Apr 14, 1997Dec 7, 1999Sealed Air CorporationFoam in bag packaging system for manual use
US5996882 *May 9, 1997Dec 7, 1999The Procter & Gamble CompanyCollapsible, foldable, stackable, and self-supporting container
US6033114 *Jan 20, 1998Mar 7, 2000Bagcraft Packaging, L.L.C.Window bag with polyester lining and method of forming same
US6054698 *Nov 1, 1996Apr 25, 2000Mast; Roy LeeMicrowave retaining package for microwave cooking
US6090028 *Sep 25, 1998Jul 18, 2000American Packaging CorporationBag and method of making the same
US6092687 *Apr 22, 1999Jul 25, 2000The Procter & Gamble CompanyCollapsible, stackable, self-supporting container with supplemental support feature
US6116501 *Apr 22, 1999Sep 12, 2000The Procter & Gamble CompanyStackable, self-supporting container with lid-alignment feature
US6139185 *May 9, 1997Oct 31, 2000The Procter & Gamble CompanyFlexible bag with selectively-activatible support-engagement feature
US6149304 *May 9, 1997Nov 21, 2000The Procter & Gamble CompanyFlexible storage bag with selectively-activatible closure
US6150647 *Jun 18, 1999Nov 21, 2000The Procter & Gamble CompanyFlexible, cushioned, high surface area food storage and preparation bags
US6164821 *May 9, 1997Dec 26, 2000The Procter & Gamble CompanyFlexible, self-supporting storage bag with hinged, framed closure
US6272813Apr 14, 1997Aug 14, 2001Sealed Air CorporationFoam in bag packaging system
US6325239Apr 22, 1999Dec 4, 2001The Procter & Gamble CompanyStackable, self-supporting container with sliding mechanical closure
US6394651Jun 18, 1999May 28, 2002The Procter & Gamble CompanyFlexible bags having enhanced capacity and enhanced stability in use
US6394652Jun 18, 1999May 28, 2002The Procter & Gamble CompanyFlexible bags having stretch-to-fit conformity to closely accommodate contents in use
US6582123 *Apr 6, 2000Jun 24, 2003Tecksom International LimitedPackage incorporating a pressure venting feature
US6588973Nov 28, 2000Jul 8, 2003James S. OmannPavement method and composition with reduced asphalt roofing waste
US6610338Dec 31, 1998Aug 26, 2003Teckson International LimitedEasy tearing bags and packaging material
US6629599Jun 18, 2001Oct 7, 2003Sealed Air CorporationFoam in bag packaging system
US7942577Dec 12, 2006May 17, 2011The Procter & Gamble CompanyFlexible bag having a drawtape closure
US8382362Oct 29, 2009Feb 26, 2013James S. OmannMethod of making paving composition without adding asphalt content oil or minimizing addition
US8610039Sep 13, 2010Dec 17, 2013Conagra Foods Rdm, Inc.Vent assembly for microwave cooking package
US8729437Jan 7, 2008May 20, 2014Con Agra Foods RDM, Inc.Microwave popcorn package, methods and product
US8735786Sep 14, 2009May 27, 2014Conagra Foods Rdm, Inc.Microwave popcorn package
US9079704Nov 23, 2010Jul 14, 2015Conagra Foods Rdm, Inc.Microwave cooking package
US9193515 *Sep 6, 2012Nov 24, 2015Frito-Lay North America, Inc.Package for microwaving dry foods
US20030106899 *Dec 12, 2002Jun 12, 2003Langen H. J. PaulContainer for microwave popcorn and method and apparatus for making the same
US20040118839 *Dec 23, 2002Jun 24, 2004Unilever Bestfoods, North America, Division Of Conopco, Inc.Package
US20040252921 *Jun 13, 2003Dec 16, 2004Winiarski Peggy B.Oven bag with pre-formed perforations
US20050276885 *Jun 10, 2004Dec 15, 2005Bennett James ASelf-venting microwaveable pouch, food item, and method of preparation
US20070237863 *Mar 28, 2007Oct 11, 2007Langen H J PContainer for microwave popcorn and method and apparatus for making the same
US20080137995 *Dec 12, 2006Jun 12, 2008The Procter & Gamble CompanyFlexible bag having a drawtape closure
US20080310772 *Mar 5, 2008Dec 18, 2008Dayton Douglas CSystems and methods for waste disposal using a disposal bag with a rectangular frame
US20090181132 *Jan 11, 2008Jul 16, 2009Conopco, Inc., D/B/A UnileverPackage
US20110100257 *Oct 29, 2009May 5, 2011Omann James SMethod of making paving composition without adding asphalt content oil or minimizing addition
US20120047854 *Apr 26, 2010Mar 1, 2012Cash Dynamics Llpbag and sealing method and apparatus
US20130084374 *Sep 28, 2012Apr 4, 2013Papier-Mettler, Inhaber Michael Mettler E.K.Bag, particularly re-baking bag, made of glassine paper or cellulose paper with a fluorine coating
US20140065265 *Sep 6, 2012Mar 6, 2014Frito-Lay North America, Inc.Package for Microwaving Dry Foods
US20150353218 *Aug 16, 2013Dec 10, 2015Windmöller & Hölscher KgMethod for producing bags
USD671012Jun 14, 2011Nov 20, 2012Conagra Foods Rdm, Inc.Microwavable bag
USD703547Jun 14, 2011Apr 29, 2014Conagra Foods Rdm, Inc.Microwavable bag
WO2001051371A1 *Jan 15, 2001Jul 19, 2001Tecksom International LimitedA package incorporating a pressure venting and related method of manufacture
U.S. Classification426/118, 53/479, 426/107, 493/220, 156/308.4, 426/234, 383/100, 493/214, 426/113, 426/415, 53/481, 53/412, 426/127
International ClassificationB65D33/01, B65D81/34
Cooperative ClassificationB65D33/01, B65D81/3469, B65D81/34, B65D2581/3421, B65D2205/00
European ClassificationB65D33/01, B65D81/34M2P, B65D81/34
Legal Events
Jul 5, 1990ASAssignment
Effective date: 19880816
Apr 17, 1995FPAYFee payment
Year of fee payment: 4
May 25, 1999REMIMaintenance fee reminder mailed
Oct 31, 1999LAPSLapse for failure to pay maintenance fees
Jan 11, 2000FPExpired due to failure to pay maintenance fee
Effective date: 19991029